Communication method taking carrier type into consideration, and apparatus therefor

ABSTRACT

The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and apparatus for a terminal to receive a downlink signal in a wireless communication system. The method includes the steps of: receiving a downlink signal through a downlink period in a subframe including the downlink period, a gap period, and an uplink period; and demodulating the downlink signal, wherein the length of the downlink period is less than or equal to half of the subframe. When the downlink signal is received on a first type of carrier, the downlink signal is demodulated using a first cell-common reference signal. When the downlink signal is received on a second type of carrier, the downlink signal is demodulated using a terminal-specific reference signal.

TECHNICAL FIELD

The present invention relates to a communication method and an apparatusfor the same when a plurality of carrier types is used in a wirelesscommunication system. More specifically, the present invention relatesto a method of transmitting/receiving signals in consideration ofcarrier type, a signaling method, a method of configuring a subframe andan apparatus therefor. The wireless communication system includes asystem supporting carrier aggregation (CA).

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services including voice and dataservices. In general, a wireless communication system is a multipleaccess system that supports communication among multiple users bysharing available system resources (e.g. bandwidth, transmit power,etc.) among the multiple users. The multiple access system may adopt amultiple access scheme such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), or SingleCarrier Frequency Division Multiple Access (SC-FDMA). In a wirelesscommunication system, a user equipment (UE) can receive information froman eNB on downlink (DL) and transmit information to the eNB on uplink(UL). Information transmitted or received by the UE includes data andvarious types of control information and there are various physicalchannels according to types and purposes of information transmitted orreceived by the UE.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for efficiently performing communication and an apparatustherefor when a plurality of carrier types is used in a wirelesscommunication system. Another object of the present invention is toprovide a method for efficiently transmitting/receiving signals inconsideration of carrier type, a signaling method, a method ofconfiguring a subframe and an apparatus therefor.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod for receiving a downlink signal by a UE supporting a plurality ofcarrier types in a wireless communication system, the method including:receiving a first downlink signal through a downlink period in asubframe including the downlink period, a gap period, and an uplinkperiod; and demodulating the first downlink signal, wherein a length ofthe downlink period is less than or equal to half the subframe, thefirst downlink signal is demodulated using a first cell-common referencesignal when the first downlink signal is received on a first typecarrier, and the first downlink signal is demodulated using aUE-specific reference signal when the first downlink signal is receivedon a second type carrier.

In another aspect of the present invention, provided herein is a UE usedin a wireless communication system, including: a radio frequency (RF)unit; and a processor, wherein the processor is configured to receive afirst downlink signal through a downlink period in a subframe includingthe downlink period, a gap period, and an uplink period and todemodulate the first downlink signal, wherein a length of the downlinkperiod is less than or equal to half the subframe, the first downlinksignal is demodulated using a first cell-common reference signal whenthe first downlink signal is received on a first type carrier, and thefirst downlink signal is demodulated using a UE-specific referencesignal when the first downlink signal is received on a second typecarrier.

The first type carrier may be a carrier through which the firstcell-common reference signal is received in all subframes and the secondtype carrier may be a carrier through which a second cell-commonreference signal is received only in some subframes.

The subframe may include 14 OFDM (Orthogonal Frequency DivisionMultiplexing) symbols and the length of the downlink period maycorrespond to 3 OFDM symbols when a normal CP (cyclic prefix) is set.

The subframe may include 12 OFDM symbols and the length of the downlinkperiod may correspond to 3 OFDM symbols when an extended CP is set.

The first downlink signal may be a PDSCH (Physical Downlink SharedChannel) signal, wherein a PDCCH (Physical Downlink Control Channel)signal corresponding to the PDSCH signal is received on the first typecarrier when the PDSCH signal is received on the first type carrier, andthe PDCCH signal corresponding to the PDSCH signal is received on acarrier different from the second type carrier when the PDSCH signal isreceived on the second type carrier.

The first downlink signal may include an uplink grant control channelsignal for scheduling an uplink data channel signal.

Advantageous Effects

According to the present invention, it is possible to efficientlyperform communication when a plurality of carrier types is used in awireless communication system. In addition, it is possible toefficiently transmit/receive signals in consideration of carrier type,perform signaling and configure a type.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a radio frame structure used in LTE-(A);

FIG. 2 illustrates a resource grid of a downlink slot;

FIG. 3 illustrates physical channels used in LTE-(A) and a signaltransmission method using the same;

FIG. 4 illustrates synchronization channel and broadcast channelstructures in a radio frame;

FIG. 5 illustrates a downlink subframe structure;

FIG. 6 illustrates a control channel and a CRS (Cell-specific ReferenceSignal or Cell-common Reference Signal) allocated to a downlinksubframe;

FIG. 7 illustrates a DM-RS (Demodulation Reference Signal) (orUE-specific RS) structure;

FIG. 8 illustrates a CA (carrier aggregation) communication system;

FIG. 9 illustrates cross-carrier scheduling;

FIG. 10 illustrates an example of allocating a PDCCH to a data region ofa subframe;

FIG. 11 illustrates a procedure of allocating resources for an E-PDCCHand receiving a PDSCH;

FIG. 12 illustrates a subframe configuration according to carrier type;

FIG. 13 illustrates special subframe configurations;

FIG. 14 illustrates DM-RS configurations according to an embodiment ofthe present invention; and

FIG. 15 is a block diagram of a BS and a UE according to an embodimentof the present invention.

BEST MODE

Embodiments of the present invention are applicable to a variety ofwireless access technologies such as Code Division Multiple Access(CDMA), Frequency Division Multiple Access (FDMA), Time DivisionMultiple Access (TDMA), Orthogonal Frequency Division Multiple Access(OFDMA), and Single Carrier Frequency Division Multiple Access(SC-FDMA). CDMA can be implemented as a radio technology such asUniversal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can beimplemented as a radio technology such as Global System for Mobilecommunications (GSM)/General Packet Radio Service (GPRS)/Enhanced DataRates for GSM Evolution (EDGE). OFDMA can be implemented as a radiotechnology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wireless Fidelity (Wi-Fi)), IEEE 802.16 (Worldwideinteroperability for Microwave Access (WiMAX)), IEEE 802.20, and EvolvedUTRA (E-UTRA). UTRA is a part of Universal Mobile TelecommunicationsSystem (UMTS). 3^(rd) Generation Partnership Project (3GPP) Long TermEvolution (LTE) is a part of Evolved UMTS (E-UMTS) using E-UTRA,employing OFDMA for downlink and SC-FDMA for uplink. LTE-Advanced(LTE-A) is evolved from 3GPP LTE.

While the following description is given, centering on 3GPP for clarity,this is purely exemplary and thus should not be construed as limitingthe present invention.

The present invention is described based on LTE-A. The concept orproposed schemes and embodiments of the present invention are applicableto other systems (e.g. IEEE 802.16m) using multiple carriers withoutrestriction.

FIG. 1 illustrates a radio frame structure used in LTE(-A).Uplink/downlink data packet transmission is performed on asubframe-by-subframe basis and a subframe is defined as a predeterminedtime interval including a plurality of symbols. 3GPP LTE supports atype-1 radio frame structure applicable to FDD (Frequency DivisionDuplex) and a type-2 radio frame structure applicable to TDD (TimeDivision Duplex).

FIG. 1( a) illustrates a type-1 radio frame structure. A downlinksubframe includes 10 subframes each of which includes 2 slots in thetime domain. A time for transmitting a subframe is defined as atransmission time interval (TTI). For example, each subframe has alength of 1 ms and each slot has a length of 0.5 ms. A slot includes aplurality of OFDM symbols in the time domain and includes a plurality ofresource blocks (RBs) in the frequency domain. Since downlink uses OFDMin 3GPP LTE, an OFDM symbol represents a symbol period. The OFDM symbolmay be called an SC-FDMA symbol or symbol period. An RB as a resourceallocation unit may include a plurality of consecutive subcarriers inone slot.

The number of OFDM symbols included in one slot may depend on CyclicPrefix (CP) configuration. CPs include an extended CP and a normal CP.When an OFDM symbol is configured with the normal CP, for example, thenumber of OFDM symbols included in one slot may be 7. When an OFDMsymbol is configured with the extended CP, the length of one OFDM symbolincreases, and thus the number of OFDM symbols included in one slot issmaller than that in case of the normal CP. In case of the extended CP,the number of OFDM symbols allocated to one slot may be 6. When achannel state is unstable, such as a case in which a UE moves at a highspeed, the extended CP can be used to reduce inter-symbol interference.

When the normal CP is used, one subframe includes 14 OFDM symbols sinceone slot has 7 OFDM symbols. The first three OFDM symbols at most ineach subframe can be allocated to a PDCCH and the remaining OFDM symbolscan be allocated to a PDSCH.

FIG. 1( b) illustrates a type-2 radio frame structure. The type-2 radioframe includes 2 half frames. Each half frame includes 4(5) normalsubframes and 1(0) special subframe. A normal subframe is used on uplinkor downlink according to uplink-downlink (UL-DL) configuration. Asubframe includes 2 slots.

Table 1 shows UL-DL configurations of subframes in a radio frame.

TABLE 1 Uplink- Downlink- downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D DD D D 6 5 ms D S U U U D S U U D

In Table 1, D denotes a downlink subframe, U denotes an uplink subframeand S denotes a special subframe. The special subframe includes DwPTS(downlink pilot timeslot), GP (guard period), and UpPTS (uplink pilottimeslot). DwPTS is used for initial cell search, synchronization orchannel estimation of a UE. UpPTS is used for channel estimation of a BSand uplink transmission synchronization of a UE. The GP is a period forcancelling interference generated on uplink due to multi-path delay of adownlink signal between uplink and downlink.

FIG. 2 illustrates a resource grid of a downlink slot.

Referring to FIG. 2, a downlink slot includes a plurality of OFDMsymbols in the time domain. One downlink slot may include 7(6) OFDMsymbols and a plurality of resource blocks (RBs). One RB may include 12subcarriers in the frequency domain. Each element on the resource gridis referred to as a resource element (RE). One RB includes 12×7(6) REs.The number N^(DL) of RBs included in the downlink slot depends on adownlink transmit bandwidth. The structure of an uplink slot may be sameas that of the downlink slot and OFDM symbols are replaced by SC-FDMAsymbols in the structure.

FIG. 3 illustrates physical channels used in LTE(-A) and a signaltransmission method using the same.

Referring to FIG. 3, when powered on or when a UE initially enters acell, the UE performs initial cell search involving synchronization witha BS in step S101. For initial cell search, the UE synchronizes with theBS and acquire information such as a cell Identifier (ID) by receiving aprimary synchronization channel (P-SCH) and a secondary synchronizationchannel (S-SCH) from the BS. Then the UE may receive broadcastinformation from the cell on a physical broadcast channel (PBCH). In themean time, the UE may check a downlink channel status by receiving adownlink reference signal (DL RS) during initial cell search.

After initial cell search, the UE may acquire more specific systeminformation by receiving a physical downlink control channel (PDCCH) andreceiving a physical downlink shared channel (PDSCH) based oninformation of the PDCCH in step S102.

The UE may perform a random access procedure to access the BS in stepsS103 to S106. For random access, the UE may transmit a preamble to theBS on a physical random access channel (PRACH) (S103) and receive aresponse message for preamble on a PDCCH and a PDSCH corresponding tothe PDCCH (S104). In the case of contention-based random access, the UEmay perform a contention resolution procedure by further transmittingthe PRACH (S105) and receiving a PDCCH and a PDSCH corresponding to thePDCCH (S106).

After the foregoing procedure, the UE may receive a PDCCH/PDSCH (S107)and transmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S108), as a general downlink/uplink signaltransmission procedure. Here, control information transmitted from theUE to the BS is called uplink control information (UCI). The UCI mayinclude a hybrid automatic repeat and request (HARQ) acknowledgement(ACK)/negative-ACK (HARQ ACK/NACK) signal, a scheduling request (SR),channel state information (CSI), etc. The CSI includes a channel qualityindicator (CQI), a precoding matrix index (PMI), a rank indicator (RI),etc. While the UCI is transmitted through a PUCCH in general, it may betransmitted through a PUSCH when control information and traffic dataneed to be simultaneously transmitted. The UCI may be aperiodicallytransmitted through a PUSCH at the request/instruction of a network.

FIG. 4 illustrates a primary broadcast channel (P-BCH) and asynchronization channel (SCH). The SCH includes a P-SCH and an S-SCH.The P-SCH carries a primary synchronization signal (PSS) and the S-SCHcarries a secondary synchronization signal (SSS).

Referring to FIG. 4, in frame configuration type-1 (FDD), the P-SCH islocated in the last OFDM symbols of slot #0 (i.e. the first slot ofsubframe #0) and slot #10 (i.e. the first slot of subframe #5) in eachradio frame. The S-SCH is located OFDM symbols immediately before thelast OFDM symbols of slot #0 and Slot #10. The S-SCH and P-SCH aredisposed in consecutive OFDM symbols. In frame configuration type-2(TDD), the P-SCH is transmitted through the third OFDM symbol ofsubframe #1/#6 and the S-SCH is located in the last OFDM symbols of slot#1 (i.e. the second slot of subframe #0) and slot #11 (i.e. the secondslot of subframe #5). The P-SCH is transmitted for every 4 radio framesirrespective of frame configuration type using the first to fourth OFDMsymbols of the second slot of subframe #0. The P-SCH is transmittedusing 72 subcarriers (10 subcarriers are reserved and 62 subcarriers areused for PSS transmission) on the basis of direct current (DC)subcarriers in OFDM symbols. The S-SCH is transmitted using 72subcarriers (10 subcarriers are reserved and 62 subcarriers are used forSSS transmission) on the basis of DC subcarriers in OFDM symbols. TheP-BCH is mapped to 72 subcarriers on the basis of 4 OFDM symbols and DCsubcarriers in one subframe.

FIG. 5 illustrates a downlink subframe structure.

Referring to FIG. 5, a maximum of 3 (4) OFDM symbols located in a frontportion of a first slot within a subframe correspond to a control regionto which a control channel is allocated. The remaining OFDM symbolscorrespond to a data region to which a physical downlink shared chancel(PDSCH) is allocated. Examples of downlink control channels used in LTEinclude a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), a physical hybrid ARQ indicatorchannel (PHICH), etc.

FIG. 6 illustrates a control channel allocated to a downlink subframe.In FIG. 6, R1 to R4 represent CRSs (Cell-specific Reference Signals orCell-common Reference Signals) for antenna ports 0 to 3. A CRS istransmitted per subframe in total-band and fixed to a specific patternin a subframe. The CRS is used for channel measurement and downlinksignal demodulation.

Referring to FIG. 6, a PCFICH is transmitted at a first OFDM symbol of asubframe and carries information regarding the number of OFDM symbolsused for transmission of control channels within the subframe. ThePCFICH is composed of 4 REGs which are equally distributed in thecontrol region on the basis of cell ID. The PCFICH indicates values of 1to 3 (or 2 to 4) and is modulated according to QPSK (Quadrature PhaseShift Keying). The PHICH is a response of uplink transmission andcarries an HARQ acknowledgment (ACK)/negative-acknowledgment (NACK)signal. The PHICH is allocated to REGs except CRS and PCFICH (first OFDMsymbol) in one or more OFDM symbols set based on PHICH duration. ThePHICH is allocated to 3 REGs distributed in the frequency domain.

A PDCCH is allocated to first n OFDM symbols (referred to as a controlregion hereinafter) of a subframe. Here, n is an integer equal to orgreater than 1 and is indicated by a PCFICH. Control informationtransmitted through a PDCCH is referred to as DCI. Formats 0, 3, 3A and4 for uplink and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B and 2C fordownlink are defined as DCI formats. Information field types, the numberof information fields and the number of bits of each information fielddepend on DCI format. For example, the DCI formats selectively includeinformation such as hopping flag, RB allocation, MCS (modulation codingscheme), RV (redundancy version), NDI (new data indicator), TPC(transmit power control), HARQ process number, PMI (precoding matrixindicator) confirmation as necessary.

The PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, information on resourceallocation of an upper-layer control message such as a random accessresponse transmitted on the PDSCH, a set of Tx power control commands onindividual UEs within an arbitrary UE group, a Tx power control command,information on activation of a voice over IP (VoIP), etc. A plurality ofPDCCHs can be transmitted within a control region. The UE can monitorthe plurality of PDCCHs. The PDCCH is transmitted on an aggregation ofone or several consecutive control channel elements (CCEs). The CCE is alogical allocation unit used to provide the PDCCH with a coding ratebased on a state of a radio channel. The CCE corresponds to a pluralityof resource element groups (REGs). A format of the PDCCH and the numberof bits of the available PDCCH are determined by the number of CCEs. TheBS determines a PDCCH format according to DCI to be transmitted to theUE, and attaches a cyclic redundancy check (CRC) to control information.The CRC is masked with a unique identifier (referred to as a radionetwork temporary identifier (RNTI)) according to an owner or usage ofthe PDCCH. If the PDCCH is for a specific UE, a unique identifier (e.g.,cell-RNTI (C-RNTI)) of the UE may be masked to the CRC. Alternatively,if the PDCCH is for a paging message, a paging identifier (e.g.,paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is forsystem information (more specifically, a system information block(SIB)), a system information RNTI (SI-RNTI) may be masked to the CRC.When the PDCCH is for a random access response, a random access-RNTI(RA-RNTI) may be masked to the CRC.

A plurality of PDCCHs can be transmitted in a subframe. Each PDCCH istransmitted using one or more CCEs each of which corresponds to 9 setsof 4 REs. 4 REs are referred to as a resource element group (REG). 4QPSK symbols are mapped to an REG. An RE allocated to a reference signalis not included in an REG and thus the number of REGs in an OFDM symboldepends on presence or absence of a cell-specific reference signal.

Table 2 shows the number of CCEs, the number of REGs and the number ofPDCCH bits according to PDCCH format.

TABLE 2 PDCCH Number of Number of Number of format CCEs (n) REGs PDCCHbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

CCEs are sequentially numbered. To simplify decoding, transmission of aPDCCH having a format composed of n CCEs can be started using a multipleof n CCEs. The number of CCEs used to transmit a specific PDCCH isdetermined by a BS according to channel quality. For example, in case ofa PDCCH assigned to a UE having a high-quality downlink channel (e.g. achannel close to the BS), only one CCE can be used to transmit thePDCCH. However, in the case of a PDCCH assigned to a UE having a poorchannel state (e.g. close to a cell edge), 8 CCEs can be used for PDCCHtransmission in order to obtain sufficient robustness. In addition, apower level of the PDCCH can be controlled according to channel quality.

In LTE(-A), positions of CCEs in a limited set in which a PDCCH can bedisposed for each UE are defined. The positions of CCEs in a limited setin which a UE can detect a PDCCH allocated thereto are referred to asthe “search space (SS)”. In LTE(-A), the size of the search spacedepends upon the PDCCH format. In addition, UE-specific and commonsearch spaces are separately defined. The UE-specific search space (USS)is set on a UE basis, whereas the common search space (CSS) is known toall UEs. The USS and CSS may overlap. If a UE has a considerably smallsearch space, no CCE is left when CCEs are allocated in the searchspace. Accordingly, a BS may not detect CCEs through which a PDCCH willbe transmitted to the UE in a predetermined subframe, which is referredto as blocking. To minimize possibility that blocking continues in thenext subframe, the start point of the USS is hopped in a UE-specificmanner.

Sizes of the CSS and USS are shown in Table 3.

TABLE 3 Number of Number of Number of PDCCH PDCCH PDCCH CCEs candidatescandidates Format (n) in CSS in USS 0 1 9 72 1 2 18 144 2 4 36 288 3 872 576

To control computational load of blind decoding based on the number ofblind decoding processes, a UE is not required to simultaneously searchfor all defined DCI formats. In general, the UE searches for formats 0and 1A at all times in the USS. Formats 0 and 1A have the same size andare discriminated from each other by a flag in a message. The UE mayneed to receive an additional format (e.g. format 1, 1B or 2 accordingto PDSCH transmission mode set by a BS). The UE searches for formats 1Aand 1C in the CSS. Furthermore, the UE may be set to search for format 3or 3A. Formats 3 and 3A have the same size as formats 0 and 1A and maybe discriminated from each other by scrambling CRC with different(common) identifiers rather than a UE-specific identifier. PDSCHtransmission schemes according to transmission mode and informationcontent of DCI formats are arranged in the following.

Transmission Mode

-   -   Transmission mode 1: Transmission from a single BS antenna port    -   Transmission mode 2: Transmit diversity    -   Transmission mode 3: Open-loop spatial multiplexing    -   Transmission mode 4: Closed-loop spatial multiplexing    -   Transmission mode 5: Multi-user MIMO    -   Transmission mode 6: Closed-loop rank-1 precoding    -   Transmission mode 7: Single-antenna port (port 5) transmission    -   Transmission mode 8: Double layer transmission (ports 7 and 8)        or single-antenna port (port 7 or 8) transmission    -   Transmission modes 9 and 10: Up to 8 layer transmission (ports 7        to 14) or single-antenna port (port 7 or 8) transmission.

DCI Format

-   -   Format 0: Resource grants for the PUSCH transmissions (uplink)    -   Format 1: Resource assignments for single codeword PDSCH        transmissions (transmission modes 1, 2 and 7)    -   Format 1A: Compact signaling of resource assignments for single        codeword PDSCH (all modes)    -   Format 1B: Compact resource assignments for PDSCH using rank-1        closed loop precoding (mode 6)    -   Format 1C: Very compact resource assignments for PDSCH (e.g.        paging/broadcast system information)    -   Format 1D: Compact resource assignments for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: Resource assignments for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: Resource assignments for PDSCH for open-loop MIMO        operation (mode 3)    -   Format 3/3A: Power control commands for PUCCH and PUSCH with        2-bit/1-bit power adjustments    -   Format 4: Resource grants for PUSCH transmission (uplink) in a        cell set to multi-antenna port transmission mode

DCI formats can be classified into a TM-dedicated format and a TM-commonformat. The TM-dedicated format refers to a DCI format set to acorresponding TM only and the TM-common format refers to a DCI formatset to all TMs. For example, DCI format 2B is a TM-dedicated DCI formatin the case of TM 8, DCI format 2C is a TM-dedicated DCI format in thecase of TM 9 and DCI format 2D is a TM-dedicated DCI format in the caseof TM 10. DCI format 1A may be a TM-common DCI.

FIG. 7 illustrates a configuration of a demodulation reference signal(DM-RS) configuration added to LTE-A. A DM-RS is a UE-specific RS usedto demodulate a signal of each layer when signals are transmitted usingmultiple antennas. Since LTE-A considers a maximum of 8 transmitantennas, a maximum of 8 layers and respective DM-RSs therefor areneeded.

Referring to FIG. 7, two or more layers share the same RE and DM-RS ismultiplexed according to CDM (Code Division Multiplexing). Specifically,DM-RSs for respective layers are spread using a spreading code (e.g. anorthogonal code such as a Walsh code or a DFT code) and then multiplexedto the same RE. For example, DM-RSs for layers 0 and 1 share the same REand are spread on 2 REs of OFDM symbols 12 and 13 using an orthogonalcode. That is, in each slot, the DM-RSs for layers 0 and 1 are spreadusing a code with SF (Spreading Factor)=2 in the time domain and thenmultiplexed to the same RE. For example, the DM-RS for layer 0 can bespread using [+1 +1] and the DM-RS for layer 1 can be spread using [+1−1]. Similarly, DM-RSs for layers 2 and 3 are spread on the same REsusing different orthogonal codes. DM-RSs for layers 4, 5, 6 and 7 arespread on REs occupied by DM-RSs 0, 1, 2 and 3 using a code orthogonalto layers 0, 1, 2 and 3. A code with SF=2 is used for DM-RS for up to 4layers and a code with SF=4 is used for DM-RSs when five or more layersare used. Antenna ports for DM-RSs are {7, 8, . . . , n+6} (n being thenumber of layers).

Table 4 shows spreading sequences for antenna ports 7 to 14 defined inLTE-A.

TABLE 4 Antenna port p [w_(p)(0) w_(p)(1) w_(p)(2) w_(p)(3)]  7 [+1 +1+1 +1]  8 [+1 −1 +1 −1]  9 [+1 +1 +1 +1] 10 [+1 −1 +1 −1] 11 [+1 +1 −1−1] 12 [−1 −1 +1 +1] 13 [+1 −1 −1 +1] 14 [−1 +1 +1 −1]Referring to Table 4, orthogonal codes for antenna ports 7 to 10 have astructure in which a length-2 orthogonal code is repeated. Accordingly,a length-2 orthogonal code is used at the slot level for up to 4 layersand a length-4 orthogonal code is used at the subframe level when fiveor more layers are used.

FIG. 8 illustrates a carrier aggregation (CA) communication system.

Referring to FIG. 8, a plurality of uplink/downlink component carriers(CCs) can be aggregated to support a wider uplink/downlink bandwidth.The CCs may be contiguous or non-contiguous in the frequency domain.Bandwidths of the CCs can be independently determined. Asymmetrical CAin which the number of UL CCs is different from the number of DL CCs canbe implemented. Control information may be transmitted/received onlythrough a specific CC. This specific CC can be referred to as a primaryCC (PCC) and other CCs can be referred to as secondary CCs (SCCs). Forexample, when cross-carrier scheduling (or cross-CC scheduling) isapplied, a PDCCH for downlink allocation can be transmitted through DLCC#0 and a PDSCH corresponding to the PDCCH can be transmitted throughDL CC#2. The term “component carrier” can be replaced by otherequivalent terms (e.g. carrier, cell, etc.).

For cross-CC scheduling, a carrier indicator field (CIF) is used.Presence or absence of the CIF in a PDCCH can be determined by higherlayer signaling (e.g. RRC signaling) semi-statically and UE-specifically(or UE group-specifically). The baseline of PDCCH transmission issummarized as follows.

-   -   CIF disabled: a PDCCH on a DL CC is used to allocate a PDSCH        resource on the same DL CC or a PUSCH resource on a linked UL        CC.    -   No CIF    -   CIF enabled: a PDCCH on a DL CC can be used to allocate a PDSCH        or PUSCH resource on a specific DL/UL CC from among a plurality        of aggregated DL/UL CCs using the CIF.    -   LTE DCI format extended to have the CIF    -   CIF corresponds to a fixed x-bit field (e.g. x=3) (when the CIF        is set).    -   CIF position is fixed irrespective of DCI format size (when the        CIF is set).

When the CIF is present, the BS can allocate a PDCCH monitoring DL CC(set) to reduce BD complexity of the UE. For PDSCH/PUSCH scheduling, aUE can detect/decode a PDCCH only in the corresponding DL CC. The BS cantransmit the PDCCH only through the monitoring DL CC (set). Themonitoring DL CC set can be set UE-specifically, UE-group-specificallyor cell-specifically.

FIG. 9 illustrates a case in which 3 DL CCs are aggregated and DL CC Ais set to a monitoring DL CC. When the CIF is disabled, each DL CC cancarry a PDCCH that schedules a PDSCH of the DL CC without the CIFaccording to LTE PDCCH rules. When the CIF is enabled through higherlayer signaling, DL CC A can carry not only a PDSCH thereof but alsoPDSCHs of other DL CCs using the CIF. DL CC B and DL CC C which are notset to monitoring DL CCs do not carry a PDCCH. Here, the term“monitoring DL CC” can be used interchangeably with terms such as“monitoring carrier”, “monitoring cell”. “scheduling carrier”,“scheduling cell”, “serving carrier”, “serving cell”, etc. A DL CC onwhich a PDSCH corresponding to a PDCCH is transmitted and a UL CC onwhich a PUSCH corresponding to a PUCCH is transmitted are referred to asscheduled carriers, scheduled cells, etc.

In LTE(-A), an FDD DL carrier and TDD DL subframe use first n OFDMsymbols of the subframe to transmit physical channels for controlinformation transmission, such as a PDCCH, PHICH, PCFICH, etc. and useother OFDM symbols for PDSCH transmission. The number of symbols usedfor control channel transmission in each subframe is signaled to the UEdynamically through a physical channel such as a PCFICH orsemi-statically through RRC signaling. The value n can be set to one toa maximum of four symbols according to subframe characteristics andsystem characteristics (FDD/TDD, system band, etc.). A PDCCH, a physicalchannel for DL/UL scheduling and control information, is transmittedthrough limited OFDM symbols in LTE. Accordingly, LTE(-A) introduces anenhanced PDCCH (E-PDCCH) that is freely multiplexed with a PDSCHaccording to FDM.

FIG. 10 illustrates an example of allocating a downlink physical channelto a subframe.

Referring to FIG. 10, a PDCCH (legacy PDCCH, L-PDCCH) according toLTE(-A) can be allocated to a control region (refer to FIGS. 6 and 7) ofa subframe. In FIG. 10, an L-PDCCH region represents a region to whichthe legacy PDCCH can be assigned. The L-PDCCH region may refer to acontrol region, a control channel resource region (i.e. CCE resource) towhich a PDCCH can be actually allocated in the control region or a PDCCHsearch space. A PDCCH can be additionally allocated to a data region(e.g. a resource region for a PDSCH) (refer to FIGS. 6 and 7). The PDCCHallocated to the data region is referred to as an E-PDCCH. As shown inFIG. 10, it is possible to mitigate scheduling restriction due tolimited control channel resources of the L-PDCCH region by additionallysecuring control channel resources through the E-PDCCH.

Specifically, the E-PDCCH can be detected/demodulated based on a DM-RS.The E-PDCCH may be transmitted over PRB pairs in the time domain. Morespecifically, a search space (SS) for E-PDCCH detection may be composedof one or more (e.g. 2) E-PDCCH candidate sets. Each E-PDCCH candidateset may occupy a plurality of (e.g. 2, 4 or 8) PRB pairs. Enhanced-CCEs(E-CCEs) constituting an E-PDCCH set may be mapped in a localized ordistributed manner (according to whether one E-CCE is distributed in aplurality of PRB pairs). When E-PDCCH based scheduling is set, asubframe in which E-PDCCH transmission/detection is performed may bedesignated. The E-PDCCH can be configured in a USS only. A UE mayattempt DCI detection only for L-PDCCH CSS and E-PDCCH USS in a subframe(referred to as an E-PDCCH subframe) in which E-PDCCHtransmission/detection is set and attempt DCI detection for L-PDCCH CSSand L-PDCCH USS in a subframe (non-E-PDCCH subframe) in which E-PDCCHtransmission/detection is not set.

In the case of E-PDCCH, a USS may be composed of K E-PDCCH sets (perCC/cell) for one UE. K may be a number equal to or greater than 1 andequal to or small than a specific upper limit. Each E-PDCCH set may becomposed of N PRBs (belonging to a PDSCH region). Here, N and PRBresources/indexes corresponding thereto may be set set-specifically (andUE-specifically). PUCCE resources/indexes respectively linked to E-CCEresources/indexes may be allocated set-specifically (andUE-specifically) by setting a start PUCCH resource/index per E-PDCCHset. Here, an E-CCE may refer to a basic control channel unit of theE-PDCCH composed of a plurality of REs (belonging to PRBs in the PDSCHregion). The E-CCE may have a configuration depending on E-PDCCHtransmission form. For example, an E-CCE for localized transmission canbe configured using REs belonging to the same PRB pairs. On the otherhand, an E-CCE for distributed transmission can be configured using REsextracted from a plurality of PRB pairs. In the case of localized E-CCE,an antenna port (AP)) may be independently used per E-CCE resource/indexin order to perform optimized beamforming for each UE. In the case ofdistributed E-CCE, the same AP set may be repeatedly used for differentE-CCEs such that a plurality of UEs can commonly use APs.

Like the L-PDCCH, the E-PDCCH carries DCI. For example, the E-PDCCH cancarry downlink scheduling information and uplink scheduling information.An E-PDCCH/PDSCH transmission/reception process and an E-PDCCH/PUSCHtransmission/reception process are identical/similar to steps S107 andS108 of FIG. 4. That is, the UE can receive an E-PDCCH and receivedata/control information through a PDSCH corresponding to the E-PDCCH.In addition, the UE can receive an E-PDCCH and transmit data/controlinformation through a PUSCH corresponding to the E-PDCCH. LTE adopts amethod of reserving a PDCCH candidate region (referred to as a PDCCHsearch space hereinafter) within a control region and transmitting aPDCCH of a specific UE in a part of the reserved PDCCH candidate region.Accordingly, the UE can acquire the PDCCH thereof within the PDCCHsearch space through blind detection. Similarly, an E-PDCCH can betransmitted through a whole reserved resource or part of the reservedresource.

FIG. 11 illustrates a procedure of allocating a resource for an E-PDCCHand receiving the E-PDCCH.

Referring to FIG. 11, the BS transmits E-PDCCH resource allocation (RA)information to the UE (S1210). The E-PDCCH RA information can include RB(or VRB (virtual resource block)) allocation information. The RBallocation information can be provided on an RB basis or RBG (resourceblock group) basis. An RBG includes two or more contiguous RBs. TheE-PDCCH RA information can be transmitted using higher layer (e.g. RRC)signaling. Here, the E-PDCCH RA information is used to reserve anE-PDCCH resource (region). The BS transmits an E-PDCCH to the UE(S1220). The E-PDCCH can be transmitted in part of the E-PDCCH resource(e.g. M RBs) reserved in step S1210 or in the entire E-PDCCH resource.Accordingly, the UE monitors a resource (region) (referred to as anE-PDCCH search space or simply search space) in which the E-PDCCH can betransmitted (S1230). The E-PDCCH search space can be provided as part ofthe RB set allocated in step S1210. Here, monitoring involves blinddecoding of a plurality of E-PDCCH candidates in the search space.

In LTE Rel-8/9/10, a CRS is transmitted through all DL subframes (SFs)(other than DL subframes configured for specific purposes (e.g. MBSFN))on carriers and control channels such as a PCFICH/PDCCH/PHICH are alsotransmitted (in some front OFDM symbols) through the DL subframes oncarriers. Accordingly, backward compatibility for providingaccess/service of legacy UEs can be secured. In next-generation systems,a carrier of a new type, through which all or some of legacysignals/channels are not transmitted due to inter-cell interferenceimprovement, carrier extendability enhancement, improved characteristics(e.g. 8Tx MIMO), etc., may be introduced. For convenience, the carrierof a new type is called a new type carrier (NCT). In contrast, a carriertype of 3GPP Rel-8/9/10 is called a legacy carrier type (LCT).

In reference signal transmission, the LCT can be used for fixed CRStransmission in some OFDM symbols at the front part of a subframe in allsubframes over a total band. When the NCT is used, fixed CRStransmission with high density can be omitted or remarkably reduced. ACRS transmitted using the NCT may be an RS having the same configurationas the CRS transmitted using the LCT, an RS having a configurationsimilar to the CRS transmitted using the LCT or an RS newly defined forthe NCT. In addition, when the NCT is employed, DL reception performancecan be improved through DL data reception based on a UE-specific DM-RSand channel state measurement based on a (configurable) CSI-RS (ChannelState Information RS) having a relatively low density and DL resourcescan be efficiently used by minimizing RS overhead. Accordingly, it ispossible to consider DL data scheduling through the NCT by operatingonly DM-RS based TMs (e.g. TM 8, 9 and 10) from among conventional TMs(that is, setting a DL TM of a UE assigned the NCT).

Even in the case of NCT, synchronization, tracking and measurement maybe required. To this end, a PSS/SSS having a configuration identical orsimilar to that in 3GPP Rel-8/9/10 can be transmitted. For example,relative order of SSs and SS transmission OFDM symbol positions can bechanged for the NCT. In addition, a CRS may be transmitted only in somesubframes and/or some frequency resources for synchronization, tracking,etc. Specifically, the CRS may be partially transmitted at specific time(e.g. in k (e.g. k=1) subframe periods at a specific interval) and aspecific frequency. Furthermore, the CRS may be transmitted only througha specific antenna port in the case of NCT. When the CRS is transmittedfor the purpose of synchronization, tracking, etc. with respect to theNCT, the CRS may not be used as an RS for demodulating a control channeland a DL signal.

FIG. 12 illustrates subframe configurations of the LCT and NCT.Referring to FIG. 12, the LCT may use an L-PDCCH and the NCT may use anE-PDCCH based on a UE-specific RS (e.g. DM-RS). In the NCT, the E-PDCCHmay be located from the first OFDM symbol of a subframe, distinguishedfrom FIG. 10. At least part of a frequency band of the LCT and at leastpart of a frequency band of the NCT may overlap (case 1) or thefrequency band of the LCT and the frequency band of the NCT may notoverlap (case 2). Case 1 may be a case in which the LCT and NCT areoperated by different eNBs and case 2 may be a case in which the LCT andNCT are operated by different eNBs or the same eNB.

Embodiment

In a TDD-based LTE(-A) system, a timing gap is necessary for DL SF=>ULSF conversion, as shown in FIG. 2( b). To this end, a special SF isincluded between a DL SF and a UL SF. The special SF can have variousconfigurations according to situations such as radio conditions and UEpositions.

Table 5 shows special SF configurations. In a special SF, DwPTS/GP/UpPTSmay be configuration in various manners according to specific SFconfiguration (simply, S configuration) and CP combination.

TABLE 5 Normal CP in DL Extended CP in DL Special UpPTS UpPTS subframeNormal Extended Normal Extended configuration DwPTS CP in UL CP in ULDwPTS in UL CP in UL 0  6592Ts 2192Ts 2560Ts  7680Ts 2192Ts 2560Ts  (3symbols) (3 symbols) 1 19760Ts 20480Ts  (9 symbols) (8 symbols) 221952Ts 23040Ts (10 symbols) (9 symbols) 3 24144Ts 25600Ts (11 symbols)(10 symbols)  4 26336Ts  7680Ts 4384Ts 5120Ts (12 symbols) (3 symbols) 5 6592Ts 4384Ts 5120Ts 20480Ts  (3 symbols) (8 symbols) 6 19760Ts 23040Ts (9 symbols) (9 symbols) 7 21952Ts — — — (10 symbols) 8 24144Ts — — —(11 symbols)

Numbers in parentheses indicate lengths of DwPTS periods, which arerepresented by the numbers of OFDM symbols. A DL SF, a UL SF and aspecial SF are respectively represented as D, U and S. Various specialSF configurations (referred to as S configurations) are supported andDwPTS and UpPTS may depend on DL/UL CP configurations.

FIG. 13 shows the numbers of OFDM symbols of DwPTS, GP and UpPTSaccording to configurations of Table 5. When a normal CP is used (i.e.14 OFDM symbols/subframes are used), the number of OFDM symbols that canbe used for downlink transmission (i.e. DwPTS) depends on Sconfiguration. Specifically, S configurations #0 and #5 can use firstthree OFDM symbols in the first slot as DwPTS. S configurations #1, #2,#3, #4, #6, #7 and #8 can use all OFDM symbols of the first slot asDwPTS.

Hereinafter, a specific SF in which DwPTS is composed of L (e.g. L=3)OFDM symbols is referred to as “shortest S (shS)”. Referring to Table 5,S configurations #0 and #5 have shS in the case of DL normal CP and Sconfigurations #0 and #4 have shS in the case of DL extended CP.Referring to FIG. 7, shS cannot be used to transmit a DM-RS due to shortDwPTS. Accordingly, a DL signal (e.g. a control channel signal or a datachannel signal) is demodulated based on a CRS in shS.

When the NCT is operated according to TDD (for at least DL), a CRS maybe set such that CRS is not transmitted through DwPTS in shS or the CRSis not used to demodulate a DL signal (e.g. a control channel signal ora data channel signal) even when the CRS is transmitted. In this case,since L OFDM symbols in DwPTS of shS cannot be used to transmit DL dataas well as (L-PDCCH based) control channels in the case of NCT, the NCTmay waste DL resources compared to the legacy carrier that providesbackward compatibility.

To solve this problem, a method of using NCT shS and a method ofconfiguring NCT shS are provided. Detailed options can be arranged asfollows. The following options can be combined in various manners exceptoptions 0 and 1 (e.g. options 2 and 3 are applied to DwPTS in shS of TDDNCT). In the following description, a PDCCH can include both the L-PDCCHand E-PDCCH unless otherwise mentioned. The following descriptionfocuses on UE operations in NCT shS and eNB operations may be performedcorresponding to the UE operations. UE/eNB operations in the LCT andoperations in a normal DL SF and a normal S SF in the NCT may beperformed according to conventional schemes (refer to FIGS. 1 to 11).Accordingly, various UE/eNB operations can be performed for subframetypes in the same carrier type according to carrier type.

Option 0: Special SF Configuration Except for shS

For the NCT, S configurations having shS (e.g. S configurations #0 and#5 in the case of DL normal CP case and S configurations #0 and #4 inthe case of DL extended CP) may not be supported. Considering that theNCT is a secondary carrier additionally aggregated with a legacy carrierand an appropriate coverage can be deployed to improve resource/powerutilization efficiency, this scheme can be usefully applied.

Option 1: No PDCCH and No DL Data in shS

Both PDCCH transmission and DL data (e.g. PDCCH) transmission may not bepermitted in DwPTS in NCT shS. Accordingly, a UE may omit blind decodingfor PDCCH detection and demodulation for DL data reception in NCT shS.

To make the best use of DL resources, operations (e.g. DL/UL granttransmission and the like) configured to be performed in DwPTS in shSmay be performed in a carrier (e.g. PCell) other than the NCT. Forexample, the UE can monitor a PDCCH in the NCT at normal SF timing (i.e.D) and monitor a PDCCH in a PCell at shS timing (cross-CC scheduling).To this end, even when the NCT is not set to the cross-CC schedulingmode, cross-CC scheduling from a (predefined) different carrier can beexceptionally permitted for shS. This scheme can be restrictivelyapplied to UL grants only since resources of U corresponding to shS arewasted when UL grant transmission is abandoned. Accordingly, in thenon-cross-CC scheduling mode, the UE can monitor both DL/UL grant PDCCHsin the NCT at normal SF timing (i.e. D) and monitor only the UL grantPDCCH in the PCell at shS timing.

Option 2: E-PDCCH Based UL Grant in shS

Only UL grant E-PDCCH transmission can be permitted in DwPTS in NCT shS.This is because resources of U corresponding to shS are wasted when ULgrant transmission is abandoned. Here, an additional DM-RS (having aconfiguration similar to a DM-RS for DL data reception) (e.g. enhancedDR-RS, E-DM-RS) may be transmitted in DwPTS for UL grant E-PDCCHdetection. Accordingly, the UE can demodulate a control channel and adata channel in the NCT on the assumption that a CRS and/or a DM-RS arepresent in D (or normal S) according to a conventional mapping schemeand attempt to demodulate/detect an E-PDCCH in shS on the assumptionthat an additional DM-RS for UL grant E-PDCCH demodulation is present inDwPTS.

Option 3: Cross-CC Scheduled DL Data in shS

Only DL data transmission, which is cross-CC-scheduled by a DL grantPDCCH transmitted through a predetermined different carrier (e.g.PCell), can be permitted in DwPTS in NCT shS. To this end, cross-CCscheduling from a different carrier can be exceptionally permitted forshS even when the NCT is set to the non-cross-CC scheduling mode. For DLdata reception, an additional DM-RS (e.g. E-DM-RS) can be transmitted inDwPTS of shS. Accordingly, the UE can demodulate a control channel and adata channel in the NCT on the assumption that a CRS and/or a DM-RS arepresent in D (or normal S) according to a conventional mapping schemeand attempt to demodulate/detect an E-PDCCH in shS on the assumptionthat an additional DM-RS for UL grant E-PDCCH demodulation is present inDwPTS.

Option 4: Cross-SF Scheduled DL Data in shS

Only DL data transmission, which is cross-CF-scheduled by a DL grantPDCCH transmitted through a DL SF (i.e. D) prior to shS, can bepermitted in DwPTS in NCT shS. To this end, the following scheme can beconsidered. In the present scheme, shS can be normalized into a DL SFthat is inappropriate to transmit a control channel signal. For example,shS can be normalized into a DL SF in which control channel signaltransmission is restricted for interference cancellation, a DL SF inwhich control channel signal transmission is restricted in order tomitigate overhead due to control channel transmission or a DL SF (e.g.MBSFN SF) in which the number of OFDM symbols through which signals canbe transmitted is limited for a specific reason. While only 2 SFs areexemplified to aid in understanding the present invention, the presentscheme can be applied to three or more SFs. For example, a controlchannel signal for at least one of DL SFs #a, #b and #c can betransmitted in D SF #a.

DL grant/DL data for each D and S: Different pieces of DL data aretransmitted in a D and an S and DL grant PDCCHs for the different piecesof DL data are individually transmitted through the D. The DL grantPDCCHs transmitted in D may include an indicator for identifying an SF(e.g. D or S) in which the DL data is transmitted. A DL grant PDCCHtransmitted in a D other than the D may not include the indicator foridentifying an SF (i.e. D or S) in which DL data is transmitted. Whenthe DL grant PDCCH includes the indicator, the indicator may be fixed toa specific value for error check. To receive DL data transmitted in shS,a DM-RS (e.g. E-EM-RS) may be transmitted in DwPTS of shS.

One DL grant over D and S/DL data for each D and S: Different pieces ofDL data are transmitted in a D and an S and one DL grant PDCCH istransmitted through the D for the two SFs. The DL grant PDCCH mayinclude an indicator for identifying an SF (e.g. both D and S, only D oronly S) in which DL data is transmitted. A DL grant PDCCH transmitted ina D other than the D may not include the indicator for identifying an SF(e.g. both D and S, only D or only S) in which DL data is transmitted.When the DL grant PDCCH includes the indicator, the indicator may befixed to a specific value for error check. To receive DL datatransmitted in shS, a DM-RS (e.g. E-EM-RS) may be transmitted in DwPTSof shS. When DL data is transmitted in both the D and S, a channelestimation result based on the DM-RS of the D may be used to receive DLdata in shS. In this case, only DL data can be received in DwPTS in shSwithout DM-RS transmission. Accordingly, whether the DM-RS (e.g.E-DM-RS) can be transmitted in DwPTS in shS is determined according tothe indicator and the UE can perform DL data demodulation inconsideration of whether the DM-RS is transmitted in DwPTS in shSaccording to the determination result. Information on DM-RS REs areexcluded from the data demodulation process when the DM-RS istransmitted in DwPTS in shS, whereas the information on the DM-RS REsmay be used for the data demodulation process when the DM-RS is nottransmitted in DwPTS in shS.

One DL grant/DL data over D and S: A single piece of DL data istransmitted through a D and an S and one DL grant PDCCH is transmittedthrough the D. The DL data may be transmitted through both the D and Sall the time or selectively transmitted in at least one of the D and S(e.g. both the D and S, only D or only S). Here, a DM-RS (e.g. E-DM-RS)may be transmitted in DwPTS of shS. In the latter case, the DL grantPDCCH corresponding to the D may include an indicator for identifying aregion in which DL data is transmitted. A DL grant PDCCH transmitted ina D other than the D may not include the indicator for identifying an SF(i.e. D or S) in which DL data is transmitted. When the DL grant PDCCHincludes the indicator, the indicator may be fixed to a specific valuefor error check. When DL data is transmitted through both the D and S, achannel estimation result based on the DM-RS of the D may be used toreceive a DL data part in shS. In this case, only DL data may bereceived in DwPTS of shS without DM-RS transmission. Accordingly,whether the DM-RS (e.g. E-DM-RS) can be transmitted in DwPTS of shS isdetermined according to the indicator and the UE can perform DL datademodulation in consideration of whether the DM-RS is transmitted inDwPTS of shS according to the determination result.

Option 5: E-PDCCH Based DL Grant and Corresponding DL Data in shS

Transmission of only a DL grant E-PDCCH and DL data corresponding to theDL grant E-PDCCH can be permitted in DwPTS in NCT shS. A DM-RS (e.g.E-DM-RS) can be transmitted in order to detect/receive the DL grantE-PDCCH and the DL data corresponding thereto.

When DL data is transmitted in DwPTS in shS, a method of determining atransport block size needs to be changed. In 3GPP Rel-8/9/10, thetransport block size is determined using a table represented bycombinations of the number of RBs and an MCS (Modulation and CodingScheme). That is, when an eNB allocates the number of RBs and MCS for DLdata reception, a transport block size (e.g. the number of bits)corresponding to [the number of RBs, MCS] is given according to apredetermined table. Since the transport block size is affected by thenumber of available OFDM symbols for DL data, a new table for thetransport block size can be defined when DL data is transmitted usingonly a small number of OFDM symbols in shS. Specifically, whenindividual DL data (e.g. codeword) is transmitted only through DwPTS ofshS, a transport block size table calculated on the assumption that 3OFDM symbols are used can be used. If one piece of DL data (e.g.codeword) is transmitted through a normal DL SF and shS, then atransport block size table, which is calculated on the assumption thatas many OFDM symbols as the sum of the numbers of OFDM symbols used inthe normal DL SF and shS, can be used.

Another method of determining the transport block size is to refer tothe conventional transport block size table defined for the normal DL SFin the legacy carrier. In this case, a value obtained by multiplying thenumber of RBs, N′_(PRB), allocated through a DL grant by a weightingfactor can be regarded as the number of RBs, N_(PRB), defined in theconventional transport block size table. The weighting factor may bedetermined as a ratio of the number of available OFDM symbols in themethod provided by the present invention (e.g. available OFDM symbols ina region corresponding to the sum of a normal DL SF and shS or only inshS) to the number of available OFDM symbols in the normal DL SF. Forexample, when individual DL data is transmitted only in DwPTS of shS,N_(PRB)=max{flooring(N′_(PRB)×α),1} can be used (0<α<1). If one piece ofDL data is transmitted through a DL SF and shS,N_(PRB)=max{flooring(N′_(PRB)×β),1} can be used (1<β<2). Here, α=0.25and β=1.25. However, the present invention is not limited thereto.

As to a control channel resource unit (e.g. E-CCE) forming an E-PDCCH(candidate), 4 or 3 E-CCEs may be mapped per PRB (Physical ResourceBlock) in consideration of RS overhead in a normal DL SF. In view ofthis, one E-CCE may be mapped per PRB considering that only 3 OFDMsymbols are available in DwPTS of shS in the case of option that permitsE-PDCCH transmission.

Referring back to FIG. 7, in the case of DM-RS for a normal CP in 3GPPRel-10, 8 antenna ports are divided into 2 CDM groups and RSs for 4antenna ports constituting each CDM group are multiplexed to an RE groupcomposed of 4 REs according to CDM using a length-4 spreading code (e.g.orthogonal code). The CDM groups are mapped to different RE groups and 4REs constituting each RE group belong to different OFDM symbols.However, the DM-RS configuration of Rel-10 cannot be reused since only 3OFDM symbols are available in DwPTS of shS. Accordingly, to transmit aDM-RS in shS, it is necessary to modify the conventional DM-RSconfiguration (FIG. 7) or define a new DM-RS configuration.

FIG. 14 illustrates DM-RS configurations according to an embodiment ofthe present invention. It is assumed that DM-RS antenna ports {7, 8, 9,10}, {7, 8} and {7} of 3GPP Rel-10 are used as 4 antenna ports, 2antenna ports and one antenna port for DM-RSs for convenience. Theexample shown in FIG. 14 is applied to NCT shS only and, in a normal DLSF or a normal S SF, a DL signal can be demodulated using theconfiguration shown in FIG. 7.

Referring to FIG. 14, in the case option that permits DM-RS (e.g.E-DM-RS) transmission, 4 or 2 antenna ports may be respectively dividedinto 2 or 1 CDM group and RSs for 2 antenna ports constituting each CDMgroup may be multiplexed to an RE group composed of 2 REs according toCDM using a length-2 spreading code. In this case, the CDM groups may bemapped to different RE groups and 2 REs constituting each RE group maybelong to different OFDM symbols. In addition, only two or one antennaport is used in NCT shS and an RS for a corresponding antenna port maybe mapped to an RE group composed of two different REs without CDM. Inthis case, RSs for respective antenna ports may be mapped to differentRE groups and 2 REs constituting each RE group may belong to differentOFDM symbols. A sequence (i.e. [+1, +1] and [−1, +1]) used for CDM ofDM-RS antenna ports {7, 8} in an extended CP in 3GPP Rel-10 can be usedas a sequence used for application of length-2 CDM.

In addition, it is possible to map only one antenna port (e.g. antennaport 7 or 8) according to FDM/TDM or without FDM/TDM (and/or withoutCDM) by limiting a DL data (and/or E-PDCCH) transmission rank (or thenumber of transport layers) in NCT shS. For example, a single antennaport based DM-RS (e.g. E-DM-RS) can be transmitted using only REscorresponding to one antenna port (e.g. antenna port 7 or 9) (that is,using FDM), using all REs corresponding to all antenna ports (e.g.antenna ports 7, 8, 9 and 10) (that is, without using FDM/TDM) or usingonly an RE belonging to one OFDM symbol (that is, using TDM) in FIG. 14.In this case, a DCI format used to schedule DL data transmitted throughNCT shS may be limited to a TM-common DCI format (e.g. DCI format 1A)since DL data is received using only one DM-RS antenna port. That is,scheduling based on TM-specific DCI format (e.g. DCI format 2C or 2D)transmission may not permitted for NCT shS. Accordingly, the UE can skipblind decoding for the TM-specific DCI format and perform blind decodingfor the TM-common DCI format (e.g. DCI format 1A) for NCT shS.

On the assumption that only antenna port #0 is used in 3GPP Rel-10, aCRS and a PSS are respectively transmitted through the first and thirdOFDM symbols in DwPTS of shS. Here, when a CRS pattern for antenna port#0 of 3GPP Rel-10 is reused for NCT CRS transmission, a problem may begenerated in application of the proposed options according to whetherthe CRS and/or PSS (and/or an SSS) are transmitted in DwPTS of NCT shS.To solve this problem, the following methods are proposed. It is assumedthat the CRS, PSS and SSS are respectively transmitted through differentOFDM symbols.

Case 1: No CRS, No PSS/SSS in shS

The CRS/PSS/SSS may not be transmitted in DwPTS of NCT shS. In thiscase, all the proposed options can be applied. A DM-RS (e.g. E-DM-RS)can be transmitted using REs of consecutive 2 OFDM symbols (e.g. firstand second OFDM symbols or second and third OFDM symbols) (refer to 14).

Case 2: No CRS, PSS or SSS in shS

Only the PSS or SSS may be transmitted and the CRS may not betransmitted in DwPTS of NCT shS. In this case, all the proposed optionscan be applied. A DM-RS (e.g. E-DM-RS) can be transmitted using REs of 2OFDM symbols (e.g. first and second OFDM symbols) other than the OFDMsymbol (e.g. third OFDM symbol) through which the PSS/SSS is transmittedin NCT shS.

Case 3: No CRS, PSS and SSS in shS

Both the PSS and SSS may be transmitted and the CRS may not betransmitted in DwPTS of NCT shS. In this case, option 1 or 4 (schemesthat do not involve DM-RS transmission) can be applied to RB regions inwhich the PSS and SSS are transmitted in NCT shS. Options and DM-RS(e.g. E-DM-RS) configurations available in case 1 can be applied toother RB regions in NCT shS.

Case 4: CRS, No PSS/SSS in shS

Only the CRS may be transmitted and the PSS and SSS may not betransmitted in DwPTS of NCT shS. In this case, all the proposed optionscan be applied. A DM-RS (e.g. E-DM-RS) may be transmitted using REs of 2OFDM symbols (e.g. second and third OFDM symbols) other than the OFDMsymbol (e.g. first OFDM symbol) through which the CRS is transmitted inNCT shS.

Case 5: CRS, PSS and/or SSS in Shortest S

The PSS and/or SSS as well as the CRS may be transmitted in DwPTS of NCTshS. In this case, option 1 or 4 (schemes that do not involve DM-RStransmission) may be applied to RB regions in which the PSS/SSS aretransmitted in NCT shS. Options and DM-RS (e.g. E-DM-RS) configurationsavailable in case 4 may be applied to RB regions other than the RBregions in which the PSS/SSS are transmitted in NCT shS.

A detailed description will be given of the E-CCE mapping method forE-PDCCH transmission. According to the E-CCE mapping method, one E-CCEmay be set/allocated for one or two PRBs or any E-CCE may not beset/allocated to a specific PRB on the basis of the number of REsoccupied by RSs (e.g. E-DM-RS) and/or SSs (PSS and/or SSS) in DwPTS ofshS. For example, an E-CCE is not allocated to a PRB in a region inwhich an SS is transmitted in NCT shS and one E-CCE is allocated for oneor two PRBs in a region in which an SS is not transmitted in NCT shS.Otherwise, one E-CCE is allocated for two PRBs in a region in which anSS is transmitted in NCT shS and one E-CCE is allocated per PRB in aregion in which an SS is not transmitted in NCT shS. Alternatively, oneE-CCE may be allocated per PRB in a region in which RSs for a pluralityof antenna ports are transmitted according to FDM/TDM (and/or withoutCDM) (without SS transmission) in NCT shS, whereas one E-CCE may beallocated for two PRBs in a region in which RSs for single or multipleantenna ports are transmitted without FDM/TDM (and/or without CDM)(without SS transmission) in NCT shS (e.g. a region in which RSs aretransmitted using all REs corresponding to all antenna ports 7, 8, 9 and10 in FIG. 14). Alternatively, one E-CCE may be set/allocated per PRBirrespective RS and SS overhead in DwPTS of NCT shS and blind decodingfor E-PDCCH detection may be performed only for E-CCE aggregation level2 or higher. Alternatively, one E-CCE may be set/allocated for two PRBsirrespective RS and SS overhead in NCT shS and blind decoding forE-PDCCH detection may be performed for all E-CCE aggregation levels(including E-CCE aggregation level 1). Furthermore, it is possible toindependently set/allocate a search space for E-PDCCH detection in NCTshS and the number of blind decoding operations per E-CCE aggregationlevel, separately from a search space (i.e. E-PDCCH PRB set) for E-PDCCHdetection in a normal DL SF.

Application of the proposed methods (options 1 to 5 according to cases 1to 5 and combinations thereof, and proposed DM-RS/E-DM-RSconfigurations) is not limited to NCT in which shS is configured and theproposed methods can be applied to a case in which an arbitrary specialSF or a special SF in which DwPTS is composed of less than N OFDMsymbols is configured in NCT. In addition, which one of the proposedmethods is applied may be set cell-specifically or UE-specifically. Nmay be 7 (normal CP) or 6 (extended CP) identical to the number of OFDMsymbols in one slot in a normal DL SF.

Even NCT may be severely interfered by various control channels/RSsignals transmitted through an L-PDCCH region on legacy carriers. Toprevent interference, an E-PDCCH start symbol position (e.g.E-PDCCH_startSym) and/or a DL data start symbol position (e.g.DL-data_startSym) for NCT may be set. If an OFDM symbol index startsfrom 0 in an SF, then E-PDCCH_startSym and DL-data_startSym may havevalues in the range of 0 to 3 (or 0 to 4). In this case, the proposedmethods can be adaptively applied to an arbitrary special SF or aspecial SF in which DwPTS is composed of less than N OFDM symbols, whichis configured in NCT, in consideration of the E-PDCCH_startSym andDL-data_startSym values.

Specifically, different methods may be applied to a case in whichE-PDCCH_startSym and DL-data_startSym have values greater than K and acase in which E-PDCCH_startSym and DL-data_startSym have values lessthan K. K may be 2 (or 3). Specifically, option 1 (or schemes that donot involve DM-RS transmission in option 4) may be applied when theE-PDCCH_startSym and DL-data_startSym values are greater than K, whereasall options may be applied when the E-PDCCH_startSym andDL-data_startSym values are less than K. Regarding the size of an REgroup to which/in which a DM-RS (e.g. E-DM-RS) is mapped/transmitted,option 1 or a 2-RE configuration based DM-RS transmission scheme(similar to FIG. 14) may be applied when the E-PDCCH_startSym andDL-data_startSym values are greater than K. That is, the DM-RS can bemapped to an RE group composed of 2 REs belonging to different OFDMsymbols. When the E-PDCCH_startSym and DL-data_startSym values are lessthan K, a 4-RE configuration based DM-RS transmission scheme similar tothat in 3GPP Rel-10 may be applied. That is, the DM-RS can be mapped toan RE group composed of 4 REs belonging to different OFDM symbols.

When shS is configured in NCT and E-PDCCH_startSym and/or DL-datastartSym have values greater than 2, the number of available OFDMsymbols may be limited to 1 or less. Here, the number of available OFDMsymbols may be calculated only on the basis of OFDM symbols (e.g. OFDMsymbols through which PSS/SSS/CRS are not transmitted) through which aDM-RS (e.g. E-DM-RS) can be transmitted. In this case, options (e.g.options 2, 3 and 5 and schemes that do not involve DM-RS transmission inoption 4) that permit E-PDCCH and/or DL data transmission in shS fromamong the proposed options may be excluded and option 1 (or schemes thatdo not involve DM-RS transmission in option 4) may be applied. When theE-PDCCH_startSym and/or DL-data startSym values are less than 2 underthe same conditions, all the proposed options can be applied since twoor more available OFDM symbols are secured.

Alternatively, when a special SF in which DwPTS is composed of 6 OFDMsymbols is configured in TDD NCT and the E-PDCCH_startSym and/orDL-data_startSym values are greater than 3, option 1 or a 2-REconfiguration based DM-RS (e.g. E-DM-RS) transmission scheme (similar toFIG. 14) may be applied since the number of available OFDM symbols islimited to three or less. When the E-PDCCH_startSym and/orDL-data_startSym values are less than 3 under the same conditions, theconventional 4-RE configuration based DM-RS transmission scheme may beapplied since four or more available OFDM symbols are secured.

Alternatively, it is possible to consider Alt 1) a method of omittingall of some UpPTSs in shS and extending DwPTSs corresponding to theomitted UpPTSs or Alt 2) a method of omitting all or some DwPTSs in shSand extending UpPTSs corresponding to the omitted DwPTSs, for TDD NCT.In the case of Alt 1, options 1 to 5 and the proposed DM-RS (e.g.E-DM-RS) configuration (e.g. FIG. 14) may be applied or modified andapplied to the extended DwPTS interval according to cases 1 to 5. In thecase of Alt 2, additional UL signal and data (e.g. SRS/PRACH and/orshort PUSCH and the like) transmission may be set/permitted for theextended UpPTS interval. When the aforementioned schemes are normalized,the proposed methods can be similarly applied to an arbitrary special SF(including shS) or a special SF in which DwPTS is composed of less thanN OFDM symbols in the case of NCT. That is, in the case of NCT, it ispossible to consider a method of omitting all or some UpPTSs in aspecial SF and extending a DwPTS interval corresponding to the omittedUpPTS interval or omitting all or some DwPTSs in a special SF andextending a UpPTS interval corresponding to the omitted DwPTS interval.

The proposed methods are not limited to the special SF. For example, theproposed methods can be similarly applied to a case in which an SF isconfigured in a form (e.g. DwPTS+Tx/Rx switching gap+UpPTS) similar tothe special SF, irrespective of FDD/TDD and/or carrier type. Forexample, a PCell and an (NCT based) SCell may be SFs respectivelyconfigured as a special SF and a DL SF in case of CA of different TDDUL-DL configurations. Here, when simultaneous transmission and receptionare not supported/permitted (that is, half-duplex), the DL SF of theSCell can be regarded as shS (DwPTS of the corresponding S) and theproposed methods can be applied in an identical/similar manner. Inaddition, the proposed methods may be similarly applied to a case inwhich DL intervals other than an interval configured for a specialpurpose (e.g. MBSFN) is set to a relatively short period in an SF. Forexample, the proposed methods can be applied to a DL interval (e.g.first m OFDM symbols (e.g. m=2) in a corresponding SF) other than aninterval in which an MBSFN signal (e.g. MBSFN data, MBSFN-RS) istransmitted (or an interval configured to transmit the MBSFN signal) inan SF configured as an MBSFN. Particularly, operations of options 1 and2, the method of case 1 and operations according to E-PDCCH relatedE-DM-RS transmission/E-CCE mapping and E-PDCCH_startSym can be applied.Furthermore, MBSFN data may be regarded as “DL data in shS” and thus theproposed methods (e.g. operation of option 3, 4 or 5) may be applied.For example, the MBSFN data can be cross-CC-scheduled by a carrier otherthan a carrier in which an MBSFN SF is configured or cross-SF-scheduledby an SF (immediately) prior to an MBSFN SF.

FIG. 15 illustrates a BS and a UE applicable to embodiments of thepresent invention.

Referring to FIG. 15, a wireless communication system includes a BS 110and a UE 120. On downlink, a transmitter is part of the BS 110 and areceiver is part of the UE 120. On uplink, the transmitter is part ofthe UE 120 and the receiver is part of the BS 110. The BS 110 includes aprocessor 112, a memory 114 and an RF unit 116. The processor 112 may beconfigured to implement the procedures and/or methods proposed by thepresent invention. The memory 114 is connected to the processor 112 andstores information related to operations of the processor 112. The RFunit 116 is connected to the processor 112 and transmits and/or receivesan RF signal. The UE 120 includes a processor 122, a memory 124, and anRF unit 126. The processor 122 may be configured to implement theprocedures and/or methods proposed by the present invention. The memory124 is connected to the processor 122 and stores information related tooperations of the processor 122. The RF unit 126 is connected to theprocessor 122 and transmits and/or receives an RF signal. The BS 110 andthe UE 120 may include a single antenna or multiple antennas.

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It will beobvious to those skilled in the art that claims that are not explicitlycited in each other in the appended claims may be presented incombination as an embodiment of the present invention or included as anew claim by subsequent amendment after the application is filed.

In the embodiments of the present invention, a description has beengiven centering on a data transmission and reception relationship amonga BS, a relay, and an MS. In some cases, a specific operation describedas performed by the BS may be performed by an upper node of the BS.Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with an MS may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘enhanced Node B (eNode B or eNB)’, ‘access point’,etc. The term ‘in’ may be replaced with the term ‘Mobile Station (MS)’,‘Mobile Subscriber Station (MSS)’, ‘mobile terminal’, etc.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to theembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the embodiments of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. For example, software code may be stored in a memory unitand executed by a processor. The memory unit is located at the interioror exterior of the processor and may transmit and receive data to andfrom the processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a method and apparatus forperforming communication when a plurality of carrier types is supportedin a wireless mobile communication system.

1. A method for receiving a downlink signal by a UE supporting aplurality of carrier types in a wireless communication system, themethod comprising: receiving a first downlink signal through a downlinkperiod in a subframe including the downlink period, a gap period, and anuplink period; and demodulating the first downlink signal, wherein alength of the downlink period is less than or equal to half thesubframe, the first downlink signal is demodulated using a firstcell-common reference signal when the first downlink signal is receivedon a first type carrier, and the first downlink signal is demodulatedusing a UE-specific reference signal when the first downlink signal isreceived on a second type carrier.
 2. The method according to claim 1,wherein the first type carrier is a carrier through which the firstcell-common reference signal is received in all subframes and the secondtype carrier is a carrier through which a second cell-common referencesignal is received only in some subframes.
 3. The method according toclaim 1, wherein the subframe includes 14 OFDM (Orthogonal FrequencyDivision Multiplexing) symbols and the length of the downlink periodcorresponds to 3 OFDM symbols if a normal CP (cyclic prefix) is set. 4.The method according to claim 1, wherein the subframe includes 12 OFDMsymbols and the length of the downlink period corresponds to 3 OFDMsymbols if an extended CP is set.
 5. The method according to claim 1,wherein the first downlink signal is a PDSCH (Physical Downlink SharedChannel) signal, wherein a PDCCH (Physical Downlink Control Channel)signal corresponding to the PDSCH signal is received on the first typecarrier when the PDSCH signal is received on the first type carrier, andthe PDCCH signal corresponding to the PDSCH signal is received on acarrier different from the second type carrier when the PDSCH signal isreceived on the second type carrier.
 6. The method according to claim 1,wherein the first downlink signal includes an uplink grant controlchannel signal for scheduling an uplink data channel signal.
 7. A UEused in a wireless communication system, comprising: a radio frequency(RF) unit; and a processor, wherein the processor is configured toreceive a first downlink signal through a downlink period in a subframeincluding the downlink period, a gap period, and an uplink period and todemodulate the first downlink signal, wherein a length of the downlinkperiod is less than or equal to half the subframe, the first downlinksignal is demodulated using a first cell-common reference signal whenthe first downlink signal is received on a first type carrier, and thefirst downlink signal is demodulated using a UE-specific referencesignal when the first downlink signal is received on a second typecarrier.
 8. The UE according to claim 7, wherein the first type carrieris a carrier through which the first cell-common reference signal isreceived in all subframes and the second type carrier is a carrierthrough which a second cell-common reference signal is received only insome subframes.
 9. The UE according to claim 7, wherein the subframeincludes 14 OFDM symbols and the length of the downlink periodcorresponds to 3 OFDM symbols when a normal is set.
 10. The UE accordingto claim 7, wherein the subframe includes 12 OFDM symbols and the lengthof the downlink period corresponds to 3 OFDM symbols when an extended CPis set.
 11. The UE according to claim 7, wherein the first downlinksignal is a PDSCH signal, wherein a PDCCH signal corresponding to thePDSCH signal is received on the first type carrier when the PDSCH signalis received on the first type carrier, and the PDCCH signalcorresponding to the PDSCH signal is received on a carrier differentfrom the second type carrier when the PDSCH signal is received on thesecond type carrier.
 12. The UE according to claim 7, wherein the firstdownlink signal includes an uplink grant control channel signal forscheduling an uplink data channel signal.